Detector for radio receiving systems



Jan. 31, 1939.

J;v M. RIDDLE. JR

DETECTOR FOR RADIO RECEIVING SYSTEMS Filed June 30, 1937 Patented Jan.31, 1939 UNITED STATES PATENT OFFCE DETECTOR FOR RADIO RECEIVING SYSTEMSApplication June 30, 1937, Serial No. 151,214

9 Claims.

The present invention relates to detectors for radio receiving systemsand has for its primary object to provide an improved detector adaptedto respond to signals of a predetermined strength.

More particularly, the invention relates to audio frequency detectors ofthe diode rectifier type and has for its further object to provide asimplified and improved delayed detection circuit in connection with thediode rectifier output circuit.

As is well understood, delayed detection of received signals preventsthe reception of noise signals in tuning a radio receiver betweenstations, and prevents the receiver from responding to signals below apredetermined strength.

In association with a diode signal rectifier, such as a second detectorof a superheterodyne receiver, a modulated signal input circuit isconnected with a diode output resistor for the rectifier, across whichresistor there are developed the direct current and audio frequencycomponents of the received signal. Either or both of these componentsare applied to the grid of a succeeding audio frequency amplifier byconnection with the output resistor.

In a preferred form of the invention, the signal rectifier or detector,and the succeeding audio frequency amplifier, may be included in thesame envelope and. may be provided with a common cathode. In circuitthere may be provided a diode output resistor, means providing a sourceof fixed biasing potential, and a bias supply connection comprisingvthree resistors in a resistance network, the arms of which bear apredetermined relation to each other, thereby to provide a predetermineddelay potential on the diode rectifier anode with respect to thecathode.

It may, therefore, be considered as a further object of the presentinvention to provide a delayed detector circuit which includes a dioderectifier having an output resistor which is included in the delaynetwork, thereby to simplify the delay circuit and to render it moreeffective in operation.

It is also a further object of the invention, to provide an improveddelayed detector circuit embodying a diode rectifier and an outputresistor therefor, wherein the output resistor may be provided as avolume control device operative to establish a variable delay potentialin accordance with variations in the volume. adjustment.

It is also a still further object of the present invention to provide adelay network for a diode signal rectifier wherein the diode outputresistor may provide unitary volume control and delay potentialadjustment means, operative to provide increased volume and delaypotential conjointly, whereby the value of the delay potential isincreased with and in proportion to volume adjustments of the volumecontrol device for increased volume or signal output.

With a system of this character, when the volume control is reduced forlow volume of signal output, additional noises are reduced thereby intuning between stations, whereas with a higher 10 level volume controladjustment, the noise suppression or detection delay is automaticallyincreased, thereby to maintain the silencing or reduction ofinterstation noise substantially uniform regardless of the volumecontrol adjustment. 1.5

The foregoing and other objects of the invention will be apparent fromthe following description of certain specific embodiments of theinvention shown in the accompanying drawing, together with otherfeatures and advantages of said invention, and its scope will be pointedout in the appended claims.

In the drawing, Figure l is a schematic circuit diagram of the second oraudio frequency detector of a superheterodyne receiver provided with avolume control and delay network embodying the invention, and

Figure 2 is a similar schematic circuit diagram of the same detectorprovided with a volume control and delay network embodying amodification of the invention shown in Figure 1.

Referring to Figure 1, an intermediate frequency amplifying channel isshown, by way of example, as the signal channel of a receiving systemterminating in an intermediate frequency output transformer 5, by whichthe intermediate frequency amplifier is coupled to the second detector6. The latter is of the diode rectifier type comprising. an anodeelectrode 1 and a cathode 8 connected with the signal input circuitcomprising the tuned secondary circuit 9 of the transformer 5.

The diode rectifier is provided with an output resistor l0 includedserially between the low potential terminal H of the input circuit 9 anda lead l2 connected with the cathode. The output resistor is providedwith a suitable intermediate frequency by-pass capacitor l3 and anintermediate frequency filter comprising a series filter resistor l4 anda second by-pass capacitor IE to to the cathode lead It! from theterminal H.

The input circuit may be traced from the anode l, which is connectedwith the high potential terminal [5 of the input circuit 9, through theinput circuit to the terminal ll, thence through the filter resistor l4and the output resistor ID to the cathode lead I2 and the cathode 8.

As is well understood, modulated signals received through theintermediate frequency amplifier output leads indicated at i! areapplied to the diode rectifier 'l--8 through the input circuit 9, andthe direct current and audio frequency components thereof appear acrossthe output resistor l0. Both the audio frequency and direct currentcomponents may be applied to a succeeding amplifier device by suitableconnection with the output resistor.

Likewise, automatic volume control potentials provided by the directcurrentcomponent of the rectified signal may be applied to the receivingsystem through a suitable automatic volume control lead l8 connectedthrough a filter IS with the terminal H or any suitable point on theresistor output network for the diode rectifier.

The cathode return to the chassis or" the apparatus is made between thelead l2 and ground or chassis 20, and includes a cathode resistor 2|,across which a potential E is established, as indicated, between theground connection 20 and the point of connection 22 between the cathodeand the rectifier output resistor W.

In the present example, the diode rectifier 1-8 is included in thecommon envelope with an audio frequency amplifier having the cathode 8in common with the diode rectifier and having a control grid 23, ascreen grid 24 and an output anode 25. The output resistor I0 isarranged as a volume control resistor, having a variable contact 26,which is connected with the control grid 23, thereby to apply the audiofrequency and direct current components of the rectified signal to thegrid 23, the amount of which components are jointly variable by theposition of the contact 26 with respect to the terminal of the outputresistor [0, which is connected with the cathode at the terminal 22. Thegrid is therefore diode biased.

The screen grid 24 and the output anode 25 receive anode potential froma suitable supply source indicated by the positive supply lead 2'1,which is connected to the screen grid 24 through a supply resistor 28and to the anode 25 through an output coupling resistor 29. The anode isalso provided with a suitable intermediate frequency by-pass capacitor30. Audio frequency signals are delivered across the resistor 29 to asuitable output circuit indicated at 3|. It will also be noted that thescreen grid is by-passed to the cathode through. a capacitor 32 and thesignal potential source represented by the resistor 2| is provided witha by-pass capacitor 33. This may be of a value only large enough toby-pass the intermediate frequency currents.

In order to provide a delay potential on the diode anode I, i. e., anegative potential with respect to the cathode. which must be overcomeby the signal potential before rectification occurs, the negative orground terminal 35 of the poten tial source 2! is connected with thediode output resistor if! at a terminal 36 forming the junction betweenthe resistors l4 and I0, through a circuit 31 which includes a seriesresistor 38. The latter is preferably variable, as indicated.

With this arrangement, the diode output resistor and the series resistor38 are connected in series across the potential source or resistorv 2|to form a network between the cathode and the diode anode, of which thediode output resistor forms a part and which results in an eifectivetapping down on a potential source for the anode connection with respectto the cathode and to the positive terminal 22 of the fixed source.

Referring to the resistor I 0 as R1 and the series resistor 38 as R2,the junction of the resistors R1 and R2 at 36 is approximately at thediode anode potential and this is lower in potential than the cathode oressentially negative with respect to the cathode by the ratio thusbiasing the diode negative and obtaining the efiect of delayeddetection. By varying the additional series resistor, the value of thedelay potential may be adjusted, but in no case is it reducible to zerobecause of the presence of the diode output resistor in the seriesnetwork comprising the resistors I0, 38 and 2|.

In addition, it will be seen that an initial negative bias is alsoplaced upon the control grid 23, which is increased as the volumecontrol contact 26 is moved in a direction to increase the volume orsignal level. The bias connection for the grid is also such that theinitial potential established on the grid is in aiding relation to thebias produced by the signal rectification.

The resistor 38 is preferably relatively high in resistance value withrespect to the diode output resistor I 0, and in a preferred embodimentthe resistor 38 may have a value variable within predetermined limits. Anormal resistor value of 470,000 ohms may be provided while the outputresistor [0 may have a resistance value of 250,000 ohms. With thiscircuit the series filter resistor I 4 may have a value of 47,000 ohmsand the resistor 2| may have a value of 2700 ohms. For use in connectionwith a tube of the type shown, which is a double diode pentode typeprovided by an RCA-6B7, the suppresser grid indicated at 4!] isconnected to the cathode and the additional diode anode indicated at 4|is connected to ground as indicated.

By providing a common cathode, a self-bias resistor as shown in thecathode lead, may be uti-- lized as a substantially fixed source ofbiasing potential for the delay potential on the diode anode, and thecircuit is greatly simplified in that the potential source and diodeoutput resistor are shunted only by a single resistor, as shown, tocomplete the delay potential network.

In case the volume control potentiometer l026 is adjusted to provide ahigh volume output, while the resistor 38 is adjusted for the low valueof delay potential on the diode anode I, signals strong enough toovercome this delay potential in tuning between stations will be heardwith loud volume and, accordingly, a modification of the circuit of Fig.1 is proposed wherein the delay potential is automatically increasedwith increasing volume adjustment, as shown in Fig. 2, wherein likereference numerals refer to the same circuits and circuit elements as inFig. 1.

Referring to Fig. 2, the combined diode rectifier and amplifier tube 6is connected to the intermediate frequency output circuit through thetransformer 5 and is provided with the same output resistor l0 and fixedbiasing potential source 2! as in the preceding figure, and the tubeelement connections are the same except for the control grid which isprovided with fixed bias from the resistor 2i through a grid resistor 42connected between the grid 23 and the negative terminal 35 of theresistor 2!. Audio frequency signals from the volume control contact 26are applied to the grid through a coupling capacitor 43, which isconnected to a lead 44 connected be tween the grid 23 and the resistor42. In this manner the grid 23 is self-biased and receives only theaudio frequency component of the rectified signals from the outputresistor of. the diode rectifier 1-43. The resistor 38 additionallyfunctions as a coupling resistor and being of high resistance value asis also the resistor 42, does not appreciably load the diode outputresistor ID, even when the volume control is maximum.

In the present example, the series resistor 38 for controlling the delaypotential is connected between the negative terminal 35 of the fixedsource 2! and the movable contact 26 of the diode output resistor NJ, asindicated at 45, whereby the amount of delay potential applied betweenthe diode anode l and the cathode 8 is determined by the amount of theresistor it included between the contact 26 and the positive terminal 22of the fixed source 2|.

It will be seen that as the contact 26 is moved upwardly, as viewed inthe drawing, to increase the volume, the effect on the delay potentialis that of tapping down on the source 2| in a nega tive direction toincrease the delay potential on the diode anode.

With this arrangement, the delay potential may be reduced to a low valuewhen the volume control is adjusted for low signal levels andinterstation noises in tuning are prevented by the fact that the volumeis reduced, whereas when the volume is increased by moving the contact26 towards the terminal 36 the delay potential is automaticallyincreased conjointly therewith to prevent response of the system tosignals causing noise when tuning between stations.

In this arrangement, the positive terminal of the means providing thefixed biasing potential is connected to the cathode of the dioderectifier, and the negative terminal of said means is connected throughthe series control resistor 38 to the movable volume control contact onthe diode output resistor, at the low potential end of which the lastnamed resistor is connected to the cathode of the diode rectifier and tosaid positive terminal.

It will be noted that when the contact 26 is substantially at the lowvolume end of the output resistor in the diode anode 'l is substantiallyat zero potential with respect to the cathode, whereby substantially nodelay potential is applied to the diode anode, and this delay potentialmay be reduced to zero when the zero volume position is reached;whereas, in the circuit of. Fig. l a zero delay potential could not beobtained be cause of the inclusion of the resistor iii in the seriescircuit for all positions of the volume control contact 26.

For this reason, the series resistor 38 and its ratio to resistor illdetermines the total amount of delay potential available when thecontact 26 is moved to the full volume control position adjacent to theterminal 36. In this position the same condition is obtained as in thecircuit of Fig. 1. The resistor 38 may then be adjusted to provide adelay potential sufficient to overcome undesired signals when tunedbetween stations, thereby reducing noise to a minimum although thevolume control contact is adjusted for maximum or relatively highvolume.

From the foregoing description, it will be seen that a delay detectoraction may be obtained in connection with a diode signal rectifier inwhich the output resistor is directly connected with the cathode, as isdesirable to prevent undesired coupling in the diode rectifier circuit,while at the same time a delay potential may be applied to the diodecircuit through a relatively high resistance connection in shunt withthe diode output resistor and a fixed potential source external to thediode rectifier circuit, and that by conmeeting the external source tothe volume control contact on the diode output resistor, a variabledelay potential may be provided conjointly with signal volume variationand in a proper direction to increase the delay potential with increasedvolume adjustment, thereby to maintain substantially constant thesuppression of interstation response of the receiving system to noiseand other undesired signals.

I claim as my invention:

1. In a radio receiving system, the combination with a diode signalrectifier having an anode and a cathode, of means providing a fixedsource of biasing potential having a positive terminal connected withthe cathode, a diode signal output resistor connected at one end withthe cathode, means providing a direct current path between the oppositeend of said output resistor and the anode, and a series resistorconnected between the negative terminal of the first named means and theanode end of said output resistor, said last named resistor having aresistance substantially higher than the resistance of the diode outputresistor such that a predetermined delay potential on said anode isprovided.

2. In a radio receiving system, the combination with a diode signalrectifier having an anode and a cathode, of means providing a fixedsource of biasing potential having a positive termnal connected with thecathode, a diode signal output resistor connected at one end with thecathode, means providing a direct current path between the opposite endof said output resistor and the anode, a volume control device providinga variable volume control connection with said output resistor, and aseries resistor connected between the negative terminal of the firstnamed means and the variable volume control connection, said last namedresistor having a resistance relative to the resistance of the diodeoutput resistor such that a delay potential on said anode is provided inaccordance with volume adjustment, and substantially zero delaypotential and volume may be obtained co-njointly.

3. In a radio receiving system, the combination with a diode signalrectifier having an anode and a cathode, of means providing a fixedsource of biasing potential having a positive terminal connected withthe cathode, a diode signal output resistor connected at one end withthe cathode, means providing a high impedance direct current pathbetween the opposite end of said output resistor and the anode, a.volume control device pro viding a variable volume control connectionwith said output resistor, and a series resistor connected between thenegative terminal of the first named means and the variable volumecontrol connection, said last named resistor having a resistancerelative to the resistance of the diode output resistor such that apredetermined total load on the diode circuit by the diode outputnetwork and a predetermined maximum delay potential on said anode isprovided, and whereby substantially zero delay potential and volume maybe obtained conjointly.

- 4. In a radio receiving system, the combination with a diode signalrectifier having an anode and a cathode, of means providing a fixedsource of biasing potential having a positive terminal connected withthe cathode, a diode signal output resistor connected at one end withthe cathode, means providing a direct current path between the oppositeend of said output resistor and the anode, a volume control deviceproviding a variable volume control connection with said outputresistor, a series resistor connected between the negative terminal ofthe first named means and the variable volume control connection, saidlast named resistor having a resistaice relative to the resistance ofthe diode output resistor such that a predetermined maximum delaypotential on said anode is provided, a signal amplifier having a controlgrid and an anode associated with said cathode, means providing a signalconveying path between said control grid and said volume controlconnection, and means providing a signal output circuit in connectionwith said last named anode.

5. In a radio signal receiving system, the combination of meansproviding a diode signal rectifier having an anode and a cathode, aresistor in circuit with said cathode, means for causing said resistorto be traversed by anode current from said system to provide apredetermined delay potential for said rectitfier, a diode outputresistor and a controlling resistor connected in series across saidcathode resistor, a signal input circuit connected with said diode anodeand having a low potential connection with the junction between saidseries connected resistors, whereby the maximum delay potential appliedto said diode anode with respect to the cathode is in the ratio of whenR1 equals the resistance of the diode output resistor and R2 equals theresistance of said controlling resistor.

6. In a radio signal receiving system, the combination of anintermediate frequency amplifier output circuit, a diode rectifierdevice coupled to said output circuit to receive amplified signalstherefrom, means for deriving the rectified direct current and audiofrequency components of said signal from said rectifier including adiode rectifier output resistor and a delay potentlal supply network forsaid rectifier including said output resistor, a biasing potentialsupply element and a controlling resistor, said last named and outputresistors being serially connected across said supply element, and saiddiode rectifier having a cathode connected between the junction of saidsupply element and the diode output resistor and having an anodeconnected at the junction between said diode output and said seriescontrolling resistors.

7. A delayed detector for radio signal receiving systems and the like,comprising in combination, a diode rectifier device having an anode anda. cathode, means for applying received signals between said anode andsaid cathode, a diode output resistor connected between the cathode andsaid last named means, means for deriving rectified signals from saidresistor, means providing a source of biasing potential having apositive terminal connected with the cathode and having a negativeterminal, a variable delay potential controlling resistor connectedbetween said negative terminal and the anode end of said outputresistor, and a filter resistor in circuit between said anode end of theoutput resistor and the signal applying means.

8. A delayed detector for radio signal receiving systems and the like,comprising in combination, a diode rectifier device having an anode anda cathode, means for applying received signals between said anode andsaid cathode, a diode output resistor connected between the cathode andsaid last named means, means for deriving rectified signals from saidresistor comprising a movable volume control contact on said resistor,means providing a source of biasing potential having a positive terminalconnected with the cathode and having a negative terminal, and a delaypotential controlling resistor connected between said negative terminaland said movable contact, said last named resistor having a relativelyhigh resistance with respect to the resistor of the diode outputresistor, whereby the delay potential applied to said diode anode isvariable conjointly with adjustment of said movable contact.

9. In a radio receiving system, the combination with a diode signalrectifier having an anode and a cathode, of means providing a fixedsource of biasing potential having a positive terminal connecteddirectly with the cathode, a diode signal output resistor connected atone end directly with the cathode, means providing a direct current pathbetween the opposite end of said output resistor and the anode, a seriesresistor connected between the negative terminal of the first named.means and the anode end of said output resistor, said last namedresistor having a resistance substantially higher than the resistance ofthe diode output resistor such that a predetermined delay potential onsaid anode is provided, and means for varying said connection for theseries resistor with the anode end of said output resistor comprising acontact movable along said output resistor toward and away from theanode end thereof.

JAMES M. RIDDLE, JR.

